Dry-type transformers are known. With this type of transformer, heat losses occurring during operation are emitted directly to the ambient air. This arrangement is in contrast to so-called oil-type transformers, in which the transformer coils are arranged in a tank filled with insulating oil and the insulating oil performs the additional function of a heat transfer medium and transfers the heat losses to the often ribbed tank wall which is in communication with the ambient air.
A further difference relating to the insulation between the individual winding layers of each coil is that, in the dry-type transformers, the sheet-metal jacket protecting the oil-type transformers from any external effects is dispensed with. Accordingly, the coils of the dry-type transformers or the surface thereof need to have comparable protection without the heat dissipation being substantially impaired thereby.
In order to meet the above requirements, synthetic resin-impregnated fibre rovings, such as those consisting of glass fibres, can be wound around the windings of the coils of dry-type transformers, in a known manner.
In this case, these fibre rovings are each applied in layers and therefore also act as insulation between the individual winding layers. The application of the individual wire layers and the insulating layers is generally performed with the aid of so-called winding apparatuses, which have a similar configuration to a lathe, wherein the subsequent coil former is clamped between a headstock and a tailstock, and the winding wire as well as the fibre rovings are each supplied from the side via a support-like guide carriage.
In order to maintain the predetermined configuration and the dimensions of the winding during manufacture of such a coil and in order to prevent synthetic resin from flowing away in an uncontrolled manner, the drying and curing of the completely wound coil is generally performed under rotation in a special curing furnace.
In order to achieve a formation of the electromagnetic field of the individual coils which is as uniform as possible, the high voltage windings of the transformer coils can be constructed in the form of so-called group windings. In this case, the winding layers are split, with respect to the entire coil length, into a plurality of groups which are located next to one another, but are connected electrically in series with one another. In turn, this procedure requires in each case an interruption in the winding when constructing the individual winding layers, i.e. it is necessary for the insulation of the winding wire associated with this layer to be removed, and once the respective associated insulation layer has been applied, the wire ends are connected to one another in DC-isolated fashion, which generally takes place by means of a soldered joint.
This procedure is time consuming and labor intensive. Furthermore, it requires an increased level of attention from the person performing this procedure.
EP 1941523 B1 discloses a method for producing a resin-insulated coil, wherein the coil is reinforced with fibres which are arranged on the coil in a solid polymer matrix. In this case, a winding layer and a fibre/polymer layer are applied alternately and repeatedly, wherein the application of the fibre/polymer layer includes the following continuously implemented steps: (i) continuous supply of at least one tape, which includes fibres and a solid polymer matrix, (ii) fusing or activation of a section of the at least one tape during the supply, (iii) pressing the fused or activated section of the tape onto the coil during the supply, and (iv) cooling the tape once it has left the heated or activated and pressed zone.
In addition, DE 4445423 A1 discloses a method in which, prior to the application of the low voltage winding, the maximum insulating thickness required for the layer insulation and the number of fibre rovings corresponding to this insulating thickness are determined. Each winding layer and the associated insulating layer are produced simultaneously with a physical offset with respect to one another. The required insulating thickness is set first via the winding feed of the fibre rovings and second via the number thereof.
A characteristic of the last mentioned method is that the fibre rovings are supplied to the winding apparatus from one side, and the winding wire is supplied from the opposite side. In other words, the fibre rovings and winding wire are supplied from different sides. This procedure has the advantage in that the rovings and the wire do not impede one another, for example in the event of a different feed. However, this entails a considerable space requirement during this procedure.